Technical Field
The present disclosure relates to a light emitting device.
Description of Related Art
Examples of a light emitting device emitting white light using a light emitting diode (which may be hereinafter referred to as an “LED”) include a light emitting device having a combination of an LED emitting blue light and a fluorescent material emitting yellow light. The light emitting device emits white light through mixing of the blue light from the LED and the yellow light from the fluorescent material excited by the blue light.
The light emitting device has a large radiation intensity in the visible region and a large luminous efficiency, but there may be some cases where sufficient radiation intensities cannot be obtained in the blue-green region and the red region. Accordingly, there is room of improvement in a general color rendering index, which is an index of the visibility of the color of the irradiated object (i.e., a color rendering property).
The evaluation procedure for the color rendering property of a light source is determined by JIS Z8726 in such a manner that the standard test colors (R1 to R15) having the prescribed reflectance characteristics are measured for colors with a test light source and the reference light source, and the color differences ΔEi (wherein i represents an integer of from 1 to 15) are numerically calculated therefrom. The upper limit of the color rendering indices Ri (wherein i represents an integer of from 1 to 15) is 100. Therefore, when the color difference between the test light source and the reference light source with a color temperature corresponding thereto is smaller, the color rendering index is increased and is close to 100.
Japanese Unexamined Patent Publication No. 2003-535477 discloses a light emitting device, in which the light emitting device uses an LED emitting blue light and, as two kinds of fluorescent materials emitting green light to yellow light, for example, a chlorosilicate fluorescent material and a garnet phosphor of Y or Tb for enhancing the color rendering property of right source. Japanese Unexamined Patent Publication No. 2008-034188 discloses a light emitting device using a fluorescent material emitting red light, in addition to a fluorescent light emitting green light to yellow light for further enhancing the color rendering property.